A new retrovirus, xenotropic murine leukaemia virus-related virus (XMRV), was identified in 2006 and an association was claimed between it and a genetic polymorphism predisposing to cancer of the prostate. In 2009 the same virus was identified in a cohort of patients with chronic fatigue syndrome (CFS). In 2010 a second related virus was identified in a separate group of CFS patients. A series of studies from disparate geographical areas have failed to substantiate this work. Most recently several papers have suggested that the detection of these viruses was explained by laboratory contamination.All papers including the wording XMRV were abstracted from the NIH library of medicine database and included in the analysis.XMRV is a newly described retrovirus whose nucleic acid has been identified in samples from patients with both prostate cancer and CFS.Opinions differ as to whether the detected nucleic acid indicates infection with this virus in this disease or whether laboratory contamination of samples accounts for its presence.An increasing number of papers now refute the association of XMRV with human disease in humans although there is some evidence of serological reactivity to the virus. While it is unlikely that XMRV is a major cause of either prostate cancer or CFS, it can infect human cells and might yet have a role in human disease.Further studies to either prove or disprove the disease association of the virus are ongoing.